When user disconnected, TCP link still alive?

[hisune]

My chat APP only 5 people online, but my server has 550 TCP link.

ss -o state established|grep :3000| wc -l

550

Why is it so? And what can I do?
Thx everyone.

[dbackowski]

See #1910

[nkzawa]

Should be fixed in v1.4.x.

[ricky65]

This issue with TCP connections not closing is still happening in v1.7.2. Can somebody look into it please.